Constant infusion of LH-RH/FSH-RH at the rate of 2.3 micrograms/hr for 24 hr in ewes induced a significant increase in serum LH concentration which reached a peak (27-30 ng/ml) by 3 hr and decreased to pretreatment levels (0.7 ng/ml) by 20 hours. Pretreatment of these ewes with or without a synthetic progestagin did not alter responsiveness of the pituitary to LH-RH/FSH-RH. Infusion with LH- RH/FSH-RH lowered pituitary content by four fold but it was not depleted of LH. No differences were noted in ovarian follicular diameter between LH-RH and saline treated ewes. Therefore, a carrier which releases LH- RH slow and constantly will probably not be useful in increasing follicular development. However, when ewes were injected with 10 micrograms LH-RH/FSH-RH at two hour intervals for 72 hours the pituitary responded by releasing LH after each injection. LH-RH/FSH-RH increased both mean luteal weight and follicular development relative to saline treated ewes. These data indicate that repeated administration of LH- RH/FSH-RH may allow the pituitary to respond longer to LH-RH treatment than constant infusion thus resulting in stimulation of ovarian follicular size. A single injection of LH-RH/FSH-RH on the last day of a clutch in hens induced premature ovulation in these birds. Thus indicating that mammalian LH-RH/FSH-RH has biological activity in the avian species. Our laboratory now has a validated double antibody RIA for LH- RH/FSH-RH and can detect LH-RH/FSH-RH levels in the serum of animals. Studies are underway to determine how LH-RH/FSH-RH serum concentrations change before LH release in estrogen treated ewes.